The majority of resist compositions currently used for the preparation of semiconductor devices are positive working resist compositions. Negative working resist compositions using cyclized rubber are difficult to increase resolution because organic solvents used as the developer cause significant swelling. By contrast, positive working resist compositions are developed with aqueous base solutions, which eliminates the swelling problem and affords superior resolution. The positive working resist compositions can thus accommodate for the desired high integration of semiconductor devices.
Most of positive resist compositions are comprised of an alkali-soluble phenolic resin and a photosensitive agent such as quinonediazidosulfonic acid ester. These positive resist compositions suffer from the precipitation of foreign matter during long-term storage because many photosensitive agents are insufficiently soluble in solvents.
To eliminate the above drawback, JP-B 45-9610 proposes a photosensitive resin having quinonediazido-sulfonic acid groups directly incorporated in an alkali-soluble resin at hydroxyl groups thereon. Since this photosensitive resin is prepared using a basic catalyst for condensation such as triethylamine, a salt of the catalyst such as the hydrochloride salt of triethylamine forms as a by-product. If a photosensitive resin composition is formulated using the photosensitive resin with the salt left therein, the use of the composition entails the problem that the salt can cause corrosion of aluminum or other metal substrates.
For preventing any loss of characteristics of the photosensitive resin by the presence of the basic catalyst itself and the salt thereof by-produced, it is proposed in JP-A 63-236030 to purify the photosensitive resin product to remove the basic catalyst and the salt thereof. This purifying and removal step is complex, cumbersome and industrially disadvantageous.
It is known from JP-A 63-237053, 9-230592 and 9-236923 that the presence of certain basic compounds in positive photoresist compositions is effective for improving the shelf stability and adhesion to substrates of the resist compositions. This suggests that if not only the salt of the basic catalyst, but the residual base are removed by the above-mentioned purifying and removal step so that only an extremely reduced amount of residual base is available, there can arise a problem that the adhesion to substrates of the resist composition, which is one of key functions, is aggravated.